1. Field of the Invention
This invention relates to a method of preparing a recording head to be used in an ink jet recording device which performs recording by forming droplets of ink by discharging ink and attaching the droplets onto a recording medium such as paper, etc., and to a method of preparing a substrate for constituting the head.
2. Related Background Art
The ink jet recording method is a recording method which performs recording by discharging ink (recording liquid) from a discharge opening provided at an ink jet recording head and attaching the ink onto a recording medium such as paper, etc. This method has many advantages. It generates little noise, is capable of high speed recording, and yet recording can be practiced on plain paper, etc., without use of a special recording paper. Various types of recording heads have been developed.
Among them, the recording head of the type which discharges ink from a discharge opening by utilizing heat energy as disclosed in Japanese Laid-open Patent Publication No. 54-59936 (corresponding to U.S. Pat. No. 4,723,129) and German Laid-open Patent Publication (DOLS) No. 2843064 has such advantages as good response to recording signals, easy multi-formation of discharge openings, etc.
Principal structure of a recording head of the type utilizing heat energy as the ink discharging energy are exemplarily shown in FIGS. 1A and 1B.
The recording head has a structure formed by bonding a substrate comprising an electrothermal transducer as heat generating means provided for converting electrical energy to heat energy to be utilized for ink discharge, arranged on a surface of a support 1 exhibiting insulating properties, and further, if necessary, an upper layer 4 as the protective layer is provided at least on the heat-generating resistor 2 and electrodes 3 positioned below a liquid path 6 and a liquid chamber 10 having an ink supply opening 9. Covering member 5 having a recession for the liquid path 6 and the liquid chamber 10, etc. formed thereon.
The discharging energy for ink discharge in this recording head is imparted by the electrothermal transducer having a pair of electrodes 3 and a heat-generating resistor 2 connected electrically to these electrodes. That is, when current is applied on the electrodes 3 to generate heat from the heat generating portion 8 of the heat-generating resistor 2, the ink in the liquid path 6 near the heat-generating portion 8 is momentarily heated to generate bubbles thereat, and through volume change by momentary volume expansion and shrinkage by generation of the bubbles, ink is discharged as a droplet from a discharge opening.
As the representative method for preparing the electrothermal transducer of the substrate in such constitution of the recording head as described above, there has been known the method as disclosed in Japanese Laid-open Patent Publication No. 59-194859 according to the steps, in which at first a heat-generating resistor layer comprising HfB.sub.2, etc. and an electrode layer comprising Al, etc. are successively laminated on an appropriate support. Next the electrode layer is etched to a predetermined shape by use of an etchant, and then the heat-generating resistor layer is further etched to a predetermined shape with the use of an etchant.
Whereas, according to such method, during etching of the heat-generating resistor layer, the etchant will attack the side face of the electrode layer already subjected to patterning, whereby curling or defect will sometimes occur on the side surface of the electrode layer. Also, as shown in FIG. 2, if the heat-generating resistor layer 2 is overetched so that the side surface of the electrode layer 3 is exposed, when a protective layer 4 is further provided, its coverage capacity will become extremely poor, giving rise to defective results such as dissolution of the electrodes by penetration of ink when assembled in the recording head.
As the means for solving such problems, for example, there is the method of subjecting the width of the electrode layer 3 to patterning smaller than the width of the heat-generating resistor layer 2 as shown in FIG. 3.
However, such method is not necessarily satisfactory in practical application or in the point of its effect.
More specifically, during patterning of the heat-generating resistor layer 2 and after patterning of the electrode layer 3, it is necessary to provide a resist mask for patterning by registration with good precision on the electrode pattern 3. Particularly, when higher densification is effected by making smaller the arrangement pitch of the heat-generating portion 8 of the heat-generating resistor 2, the difference in width (W) between the electrode layer 3 and the heat-generating resistor layer 2 must be formed on the order of, for example, 1 .mu.m or less, and registration of the resist mask with good precision in such case is technically difficult, whereby generation of defective registration will often occur resulting in lowering of yield.
Also, since patterning of the heat-generating resistor layer is effected in the wet step by use of an etchant, defective patterning of the heat-generating resistor layer due to the peeling of the etching resist or the battery reaction between the heat-generating resistor layer and the electrode layer will sometimes be generated.